Polymeric stent polishing method and apparatus

ABSTRACT

A method and apparatus for simultaneously polishing the inner and outer surfaces of an unpolished polymeric stent using a heat process. The unpolished stent can be mounted, for example, on a “spiral-mandrel,” a tubular helical structure with gaps in between a series of coils of the structure. Heat from a heat source can then applied to the spiral-mandrel at a range between the glass transition temperature and melting temperature of the polymer of the stent.

CROSS REFERENCE To RELATED APPLICATION

The present application is a division of U.S. patent application Ser.No. 12/643,679 filed Dec. 21, 2009 which is a continuation of U.S.patent application Ser. No. 11/194,089, now U.S. Pat. No. 7,658,880,filed Jul. 29, 2005, the entire contents of each is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

A treatment involving a stent includes both delivery and deployment ofthe stent. “Delivery” refers to introducing and transporting the stentthrough a lumen of a tubular organ to a region requiring treatment.“Deployment” corresponds to the expanding of the stent within the lumenat the treatment region. Delivery and deployment of a stent may beaccomplished by positioning the stent about one end of a catheter,inserting the end of the catheter through the skin into the lumen,advancing the catheter in the lumen to a desired treatment location,expanding the stent at the treatment location, and then removing thecatheter from the lumen.

In the case of a balloon-expandable stent, the stent is mounted about aballoon disposed on the catheter. Mounting the stent typically involvescompressing, or crimping, the stent onto the balloon. The stent is thenexpanded by inflating the balloon. The balloon may then be deflated andthe catheter withdrawn. In the case of a self-expanding stent, the stentmay be secured to the catheter via a retractable sheath or a sock. Whenthe stent is in a desired body location, the sheath may be withdrawnallowing the stent to self-expand.

Stents have been made of many materials including metals and polymers.Polymer materials include both nonbioerodable and bioerodable plasticmaterials. In some applications, a polymeric bioerodable stent may bemore advantageous than a metal stent due to its biodegradeability andgreater flexibility relative to the metal stent. The cylindricalstructure of a stent is typically composed of a scaffolding thatincludes a pattern or network of interconnecting structural elements orstruts. The scaffolding can be formed from wires, tubes, or planar filmsof material rolled into a cylindrical shape. In addition, a medicatedstent may be fabricated by coating the surface of either a metallic orpolymeric scaffolding with a polymeric carrier. The polymeric carriercan include an active agent or drug. Furthermore, the pattern that makesup the stent allows the stent to be radially expandable andlongitudinally flexible. Longitudinal flexibility facilitates deliveryof the stent and rigidity functions to hold open a lumen of a tubularorgan. Generally, the pattern should be designed to maintain thelongitudinal flexibility and rigidity required of the stent. The stentshould also have adequate strength in the circumferential direction.

A number of techniques have been suggested for the fabrication of stentsfrom tubes and planar films or sheets. Examples of such techniquesinclude laser cutting or etching a pattern onto a material. Lasercutting may be performed on a planar film of a material which is thenrolled into a tubular configuration. Alternatively, a desired patternmay be etched directly onto a tube. Other techniques involve cutting adesired pattern into a sheet or a tube via chemical etching orelectrical discharge machining. Laser cutting of stents has beendescribed in a number of publications including U.S. Pat. No. 5,780,807to Saunders, U.S. Pat. No. 5,922,005 to Richter and U.S. Pat. No.5,906,759 to Richter.

With respect to polymeric stents, a number of manufacturing methods havebeen employed. In one method, the polymeric stent may be formed by lasercutting a flat polymeric sheet in the form of rings and links,subsequently rolling the pattern into the shape of the cylindrical stentand then providing a longitudinal weld to form the stent. In anothermethod, a flat polymeric sheet may be chemically etched and thensubsequently rolled and welded to form the polymeric stent.Additionally, a polymeric wire may be coiled to form a polymeric stent.In yet another method, a polymeric stent may be formed from a tube bylaser cutting a pattern of cylindrical rings and connecting rings in thetube itself. See, e.g., U.S. Pat. No. 6,585,755 to Jackson et al.

In the manufacturing processes previously described, a resultant “rough”stent will be produced. That is, the struts forming the stent willtypically have an approximate “square” cross-section with four distinctsurfaces as a result of the cutting or etching process. A typical stentis then polished to “round out” the sharp corners in addition tosmoothing out the surface of the stent.

Various methods exist for polishing metal stents. Typical polishingmethods include electropolishing using an electrolyte solution or laserpolishing using a laser, described in more detail in U.S. Pat. No.5,344,425 to Sawyer, U.S. Pat. No. 6,679,980 to Andreacchi, U.S. Pat.No. 6,375,826 to Wang et al. and U.S. Pat. No. 6,492,615 to Flanagan.The use of abrasives to polish stents is disclosed in U.S. Pat. No.5,746,691 to Frantzen, U.S. Pat. No. 5,788,558 to Klein and U.S. Pat.No. 6,086,455 to Frantzen.

Polymeric stents may undergo polishing as well. A polymeric stent may bepolished using solvents. Solvent polishing smoothes out the surfaces androunds out “sharp corners” of the struts and connecting elements of apolymeric stent; however, adequately removing the solvent and minimizingthe residual solvent are problems associated with this method.Accordingly, methods are needed for polishing polymeric stents.

SUMMARY OF THE INVENTION

Methods for simultaneously polishing the abluminal surface and theluminal surface of an implantable medical device are disclosed herein.The implantable device may be a metal or polymeric stent, for example.The polymeric stent may be a bioerodable, biodegradable or bioadsorbablepolymer. In one embodiment, a wire is wrapped around the abluminalsurface of a mandrel (of a stent manufacturing device), and the mandrelis thereafter removed forming a hollow spiral-mandrel (orhelical-mandrel). An unpolished stent is then mounted onto the abluminalsurface of the hollow spiral-mandrel. The stent is then subjected toheat treatment, such as heat flashing from a heat source, resulting insubstantially or completely smooth surfaces and rounded corners of theunpolished stent struts and connecting elements on both the abluminaland luminal surfaces of the stent thereof.

The hollow spiral-mandrel allows heat to pass between the spaced coilsof the spiral-mandrel so that the heat reaches the luminal surface ofthe stent. As a result, the abluminal surface and luminal surface of thestent are simultaneously polished. That is, the spiral-mandrel promotesheat transfer to ensure that all four corners of a strut or connectingelement are simultaneously rounded out.

In another aspect of the invention, a porous sheath is used in a processto simultaneously polish the abluminal surface and luminal surface ofthe stent. The sheath serves the same function as that described for thespiral-mandrel, namely, to allow heat to pass through the pores of theporous sheath so that the heat may reach the luminal surface of thestent. It should be understood that the present invention encompasses avariety of different embodiments of the device which provides adequateheat transfer to the luminal surface of the stent for polishing of“sharp corners” therein.

According to another aspect of the invention, a method of polishing apolymeric stent includes: providing a structure with a series of gaps,the structure having an inner surface, an outer surface and a lumen;mounting a stent, the stent having a stent inner surface, a stent outersurface and a stent lumen, onto the structure; and after the mounting,subjecting the stent to heat from a heat source. The heat polishes boththe inner and outer surfaces of the polymeric stent. The structure canbe, for example, tubular.

According to a further aspect of the invention, a method of polishing apolymeric stent includes: mounting a polymeric stent on aspiral-mandrel; and after the mounting, subjecting the stent to heatfrom a heat source.

According to a still further aspect of the invention, a method ofreducing the stress concentration on angles of struts on a polymericstent includes: positioning a stent on a spiral-mandrel, the stentincluding a plurality of struts, the struts having an approximate squarecross-section; and after the positioning, applying heat to a surface ofthe stent from a heat source to smooth out the angles or corners of thestruts. The heat can be distributed evenly across the body of the stentor can be specifically directed or concentrated at particular areas ofthe stent. A concentrated application is preferable when some areas needmore polishing than other sections of the stent.

According to a yet another aspect of the invention, a method forsimultaneously polishing an entire surface of a polymeric stentincludes: wrapping a wire around a mandrel to form a spiral-mandrel;after the wrapping, removing the mandrel from the spiral-mandrel;mounting an unpolished stent on the spiral-mandrel, the stent includinga luminal surface, and an abluminal surface; and after the mounting,subjecting the stent to intense heat from a heat source, so that theluminal surface and the abluminal surface are polished.

According to a further aspect of the invention, a method of heatpolishing a tubular medical device includes: subjecting a tubularmedical device, which is positioned on and around a mandrel having asolid mandrel surface and at least one spacer on the mandrel surface tohold the device spaced out from the mandrel surface, to external heat,such that the heat passes through openings in the device and heatpolishes internal surfaces of the device spaced out from the mandrelsurface.

According to yet another aspect of the invention, a device for heatpolishing an inner surface of a stent includes: a helical structurehaving an outer surface, an inner surface and a lumen, the helicalstructure including a series of coils. The helical structure can includea series of spaces in between the series of coils, and there are atleast two coils. In some embodiments, there are at least three to tencoils, and can be more than ten coils. The spacing between the coils canbe at least 0.005″. In some embodiments, the device can have a braidedconfiguration, an interconnected ring configuration or a porous tubeconfiguration.

According to a further aspect of the invention, equipment for polishingluminal surfaces of a medical device includes: a means for holding thedevice relative to a heat source such that the heat can access luminalsurfaces of the device. In some embodiments, the device can be apolymeric stent. The equipment can include means for moving the deviceaxially and/or rotationally relative to the source. Further, theequipment can include a conveyor for conveying the device past thesource, and the source can be a heat chamber. In some embodiments, theheat source can encircle the device.

Other objects and advantages of the present invention will become moreapparent to those persons having ordinary skill in the art to which thepresent invention pertains from the foregoing description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an unpolished stent which can be used pursuant tomethods and apparatuses of the present invention.

FIG. 2 shows an enlarged portion of a strut of the stent of FIG. 1.

FIG. 3 shows an enlarged cross-sectional view of the strut of FIG. 2taken on line 3-3.

FIG. 4A illustrates a mandrel and coiling wire, which can be usedpursuant to the present invention.

FIG. 4B shows the coiling wire of FIG. 4A wrapped around the mandrel ofFIG. 4A.

FIG. 4C illustrates a spiral-mandrel formed by coiling the wire aroundthe mandrel of FIG. 4A in accordance with one embodiment of the presentinvention and subsequently separating the mandrel therefrom.

FIG. 5 illustrates another embodiment of a mandrel of the presentinvention.

FIG. 6 illustrates yet another embodiment of a mandrel of the presentinvention.

FIG. 7A illustrates yet another embodiment of a mandrel of the presentinvention.

FIG. 7B illustrates a variation of the mandrel of FIG. 7A.

FIG. 8A illustrates an embodiment of a method of the present inventionin which a stent is mounted on the spiral-mandrel of FIG. 4C forpolishing thereof.

FIG. 8B illustrates an embodiment of a method of the present inventionin which a stent is mounted on the spiral-mandrel assembly of FIG. 4Bfor polishing thereof.

FIG. 9A is an enlarged cross-sectional view taken on line 9A-9A of FIG.8A of the mandrel of FIG. 4C with a stent mounted thereon.

FIG. 9B is an enlarged cross-sectional view taken on line 9B-9B of FIG.8B of the spiral-mandrel of FIG. 4B with a stent mounted thereon.

FIG. 10A illustrates a method of the present invention in which a stentis mounted on a hypotube for heat polishing of the stent.

FIG. 10B illustrates a method (and assembly) of the present invention inwhich a stent is moved rotationally and/or axially relative to a heatsource for heat polishing of the stent.

FIG. 11 illustrates another method of the present invention in which astent is mounted on a conveyor for polishing of the stent at a heatingstation.

FIG. 12A is a cross-sectional view of a further method of the presentinvention in which a stent is mounted on a mandrel (or one of thealternative embodiments herein) for heat polishing thereof.

FIG. 12B is a view similar to FIG. 12A of a variation thereof.

FIG. 13 illustrates a still further alternative embodiment of a methodof the present invention in which a stent is mounted on a heatconducting sleeve or tube for heat polishing of the stent.

FIG. 14 shows an enlarged portion of a strut of a stent after havingbeen polished in accordance with any of the embodiments of the presentinvention.

FIG. 15 shows an enlarged cross-sectional view of the strut of FIG. 14taken on line 15-15 thereof.

FIG. 16 illustrates a stent polished pursuant to a method of the presentinvention on a catheter and in an expanded state.

FIG. 17 illustrates the stent of FIG. 16 in a crimped state on thecatheter of that figure.

FIG. 18 illustrates the stent of FIG. 17 in an expanded state in abodily lumen.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates a stent 10, which may be metal or polymeric,preferably polymeric. In either form, the stent 10 can includes amultitude of struts 12 and connecting elements 14, with interstitialspaces 16 located therebetween. Additionally, with respect to a stentconstructed from polymer material, the stent 10 may be manufactured by avariety methods, including but not limited to: (a) laser-cutting a flatpolymeric sheet in the form of rings and links, and then subsequentlyrolling the pattern into the shape of the cylindrical stent andproviding a longitudinal weld to form the stent; (b) chemically etchinga flat polymeric sheet and then subsequently rolling and welding to formthe polymeric stent; (c) coiling a polymeric wire to form a polymericstent, and (d) laser-cutting a pattern of cylindrical rings andconnecting rings onto the tube itself. See, e.g., U.S. Pat. No.6,585,755 to Jackson et al. It has been found, however, that polymericstents manufactured by conventional polishing processes may besusceptible to cracking.

A polymeric stent 10 can be made from and/or coated with a biostablepolymer or a bioerodable, biodegradable, bioadsorbable polymer or anycombination thereof. Bioerodable, biodegradable or bioadsorbable areintended to be used interchangeably unless otherwise indicated.Additionally, the length of the stent may vary. In general, a coronarystent will be in a range from eight mm to thirty-eight mm. In oneembodiment, the stent 10 may be twelve mm in length. Peripheral stents(being larger vessels) can be as long as one-hundred and fifty mm. Also,the stent inner diameter (“ID”) can range anywhere between two mm tofour mm for coronary stents and five mm to twenty mm for peripheralstents. In some embodiments, a polymeric stent can include othermaterials, such as layers or deposits of metallic material which can bebioerodable.

Representative examples of polymers which may comprise a polymeric stentand/or a coating thereon are, but are not limited to, fluorinatedpolymers or copolymers such as poly(vinylidene fluoride),poly(vinylidene fluoride-co-hexafluoro propene),poly(tetrafluoroethylene), and expanded poly(tetrafluoroethylene);poly(sulfone); poly(N-vinyl pyrrolidone); poly(aminocarbonates);poly(iminocarbonates); poly(anhydride-co-imides), poly(hydroxyvalerate);poly(L-lactic acid); poly(L-lactide); poly(caprolactones);poly(lactide-co-glycolide); poly(hydroxybutyrates);poly(hydroxybutyrate-co-valerate); poly(dioxanones); poly(orthoesters);poly(anhydrides); poly(glycolic acid); poly(glycolide); poly(D,L-lacticacid); poly(D,L-lactide); poly(glycolic acid-co-trimethylene carbonate);poly(phosphoesters); poly(phosphoester urethane); poly(trimethylenecarbonate); poly(iminocarbonate); poly(ethylene); and any derivatives,analogs, homologues, congeners, salts, copolymers and combinationsthereof.

In some embodiments, the polymers include, but are not limited to,poly(propylene) co-poly(ether-esters) such as, for example,poly(dioxanone) and poly(ethylene oxide)/poly(lactic acid);poly(anhydrides), poly(alkylene oxalates); poly(phosphazenes);poly(urethanes); silicones; poly(esters); poly(olefins); copolymers ofpoly(isobutylene); copolymers of ethylene-alphaolefin; vinyl halidepolymers and copolymers such as poly(vinyl chloride); poly(vinyl ethers)such as, for example, poly(vinyl methyl ether); poly(vinylidene halides)such as, for example, poly(vinylidene chloride); poly(acrylonitrile);poly(vinyl ketones); poly(vinyl aromatics) such as poly(styrene);poly(vinyl esters) such as poly(vinyl acetate); copolymers of vinylmonomers and olefins such as poly(ethylene-co-vinyl alcohol) (EVAL);copolymers of acrylonitrile-styrene, ABS resins, and copolymers ofethylene-vinyl acetate; and any derivatives, analogs, homologues,congeners, salts, copolymers and combinations thereof.

In some embodiments, the materials can also include, but are not limitedto, poly(amides) such as Nylon 66 and poly(caprolactam); alkyd resins;poly(carbonates); poly(oxymethylenes); poly(imides); poly(ester amides);poly(ethers) including poly(alkylene glycols) such as, for example,poly(ethylene glycol) and poly(propylene glycol); epoxy resins;polyurethanes; rayon; rayon-triacetate; biomolecules such as, forexample, fibrin, fibrinogen, starch, poly(amino acids); peptides,proteins, gelatin, chondroitin sulfate, dermatan sulfate (a copolymer ofD-glucuronic acid or L-iduronic acid and N-acetyl-D-galactosamine),collagen, hyaluronic acid, and glycosaminoglycans; other polysaccharidessuch as, for example, poly(N-acetylglucosamine), chitin, chitosan,cellulose, cellulose acetate, cellulose butyrate, cellulose acetatebutyrate, cellophane, cellulose nitrate, cellulose propionate, celluloseethers, and carboxymethylcellulose; and any derivatives, analogs,homologues, congeners, salts, copolymers and combinations thereof.

In some embodiments, the polymer can be a poly(ester amide), apoly(lactide) or a poly(lactide-co-glycolide) copolymer; and anyderivatives, analogs, homologues, congeners, salts, copolymers andcombinations thereof.

In some embodiments, the polymers can be biodegradable, bioerodableand/or bioadsorbable. Examples of biodegradable polymers include, butare not limited to, polymers having repeating units such as, forexample, an α-hydroxycarboxylic acid, a cyclic diester of anα-hydroxycarboxylic acid, a dioxanone, a lactone, a cyclic carbonate, acyclic oxalate, an epoxide, a glycol, an anhydride, a lactic acid, aglycolic acid, a lactide, a glycolide, an ethylene oxide, an ethyleneglycol, and any derivatives, analogs, homologues, congeners, salts,copolymers and combinations thereof.

In some embodiments, the biodegradable polymers include, but are notlimited to, polyesters, poly(ester amides); poly(hydroxyalkanoates)(PHA), amino acids; PEG and/or alcohol groups; polycaprolactones,poly(D-lactide), poly(L-lactide), poly(D,L-lactide), poly(meso-lactide),poly(L-lactide-co-meso-lactide), poly(D-lactide-co-meso-lactide),poly(D,L-lactide-co-meso-lactide), poly(D,L-lactide-co-PEG) blockcopolymers, poly(D,L-lactide-co-trimethylene carbonate), polyglycolides,poly(lactide-co-glycolide), polydioxanones, polyorthoesters,polyanhydrides, poly(glycolic acid-co-trimethylene carbonate),polyphosphoesters, polyphosphoester urethanes, poly(amino acids),polycyanoacrylates, poly(trimethylene carbonate), poly(imino carbonate),polycarbonates, polyurethanes, copoly(ether-esters) (e.g. PEO/PLA),polyalkylene oxalates, polyphosphazenes, PHA-PEG, and any derivatives,analogs, homologues, salts, copolymers and combinations thereof.

In other embodiments, the polymers can be poly(glycerol sebacate);tyrosine-derived polycarbonates containing desaminotyrosyl-tyrosinealkyl esters such as, for example, desaminotyrosyl-tyrosine ethyl ester(poly(DTE carbonate)); and any derivatives, analogs, homologues, salts,copolymers and combinations thereof.

In some embodiments, the polymers are selected such that theyspecifically exclude any one or any combination of any of the polymerstaught herein.

An enlarged portion of a strut 12 of stent 10 is shown in FIG. 2. Beforepolishing, a cross-section of a typical strut 12 has a “square” shape.That is, in an unpolished state, the strut 12 can include four surfaces,sides or walls 18 with four approximately ninety degree angle “sharpcorners” 22. This shape is primarily as a result of the cutting oretching step in the manufacturing process.

In FIG. 3, a cross-section of the strut 12 depicted in FIG. 2 is showntaken on line 3-3. If the strut 12 is left unpolished, the sharp corners22 may result in the manifestation of cracks 26 in the stent 10 whencrimped on a catheter or mandrel, or during expansion when deliveredinto a bodily lumen (see FIGS. 16, 17 and 18, discussed later herein).The cracks 26 are due to the high stress concentration, or “stressrisers,” initiated from the sharp corners 22. Such cracks may jeopardizethe integrity of the stent 10 itself, thereby causing an increased riskof damage to a bodily lumen during delivery of the stent, the collectionof plaque and other deposits on the stent and balloon bursts inballoon-expandable stents, for example.

In general, the present invention is directed to methods of polishingstents to reduce or eliminate stress risers. Thus, FIGS. 4A-4Cillustrate one form of creating a “spiral-mandrel” used in oneembodiment of a method of polishing a polymeric stent of the presentinvention. In FIG. 4A, a mandrel 28 and coiling wire 30 are shown. Themandrel 28 may be polymeric or metal, with a typical outer diameter ofapproximately 0.010″ to 0.050″. In addition, the coiling wire 30 may becomposed of a heat conductive poor heat conductive or non-heatconductive material, or a combination thereof. For example, in oneembodiment, the coiling wire 30 may be heat conductive, such asstainless steel, and coated with a non-heat conductive substance, suchas parylene. A non-stick coating can also be used, such as Teflon. Inanother embodiment, the coiling wire 30 may be uncoated stainless steelor titanium, thus retaining heat conductive properties. In someembodiments, the coiling wire can be from or coated with aluminum,copper, silver and/or gold. Additionally, the coiling wire 30 can have athickness of approximately 0.020″ to 0.050″, preferably 0.025″.

In FIG. 4B, coiling wire 30 is shown wrapped around the mandrel 28 in ahelical manner forming a helical assembly 34. A space of approximately0.005″ to 0.050″, preferably 0.025″, may exist between the coils of thehelical assembly 34. In some embodiments, the number of coils may varyfrom two to fifteen, preferably ten. In other embodiments, the number ofcoils may be practically unlimited for an embodiment with a continuousmandrel and multiple stents on it similar to a conveyor.

In FIG. 4C, the mandrel 28 is shown being removed from the helicalassembly 34 (depicted by arrow 36), resulting in a “spiral-mandrel” 32 awith a lumen 44 therein. The spiral-mandrel can be, for example, atleast one inch long. The inner diameter of the spiral-mandrel 32 adepends on the diameter of the wire 30 used to make it. The outerdiameter of the spiral-mandrel 32 a depends on the inner diameter of thestent 10. The abluminal surface of the spiral-mandrel 32 a can betightly controlled to match the luminal surface of the unpolished stent10 in order to provide an appropriate fit between the spiral-mandrel 32a and the stent 10. Ultimately, the spiral-mandrel 32 a functions topromote adequate heat transfer to ensure that all four corners 22 of astrut 12 cross-section are properly “rounded out,” as will be more fullydiscussed below.

In an alternative embodiment, a series of interconnected rings 32 b witha lumen 44 therein, as illustrated in FIG. 5, may be used as the deviceto effectuate heat transfer. The interconnected rings 32 b can belaser-cut or chemically etched from a pattern of a tube or flat sheet ofmetal (and rolled into a tube therefore). Alternatively, the rings 32 bcan be interconnected by a secondary process such as welding. In anotheralternative embodiment, a porous sheath 32 c with a lumen 44 therein, asillustrated in FIG. 6, may be used as the device to effectuate heattransfer. The porous sheath 32 c may be manufactured by a variety ofmethods, including laser-cutting and chemically etching, by methodsknown to those skilled in the art. Porous sheath 32 c can includediscrete or interconnected holes that can extend through the body of thesheath 32 c so as to provide a passage from the outer surface of thesheath 32 c to the lumen 44. This allows the heat to enter and circulatewithin the lumen 44. Mandrels 32 b and 32 c can be made or coated withthe same materials discussed above.

Referring to FIG. 7A, a further embodiment of the present invention canbe a tubular braided device as shown generally at 35 having braidedmembers or “wires” 35 a. The criss-crossing wires 35 a can be fixed toone another to prevent the braided device from stretching and therebyhaving its diameter narrow. One way of “fixing” wires 35 a is bywelding. The braided geometry can be simple or complex by adjusting theangles between wires. An alternative thereof, which is illustratedgenerally at 35 b in FIG. 7B, is also a braided construction butincludes longitudinal struts 35 c, which can run the length of thebraided device or mandrel. The longitudinal struts 35 c can act asreinforcement for the criss-crossing wires 35 a. Embodiments of FIGS. 5,6 and 7 can be made from heat conductive, poor heat conductive, non-heatconductive or a combination thereof as discussed above with respect tothe spiral mandrel 32 a. For example, porous sheath 32 c can be madefrom a heat conductive metal coated with a non-heat conductive ornon-stick material.

In FIGS. 8A and 8B, the spiral-mandrel 32 a with the stent 10 positionedthereon is shown mounted on a stent manufacturing device 38. The stentmanufacturing device 38 can include a motor 38 a for rotating the stent,a motor 38 b for moving the stent longitudinally and a support members38 c and 38 d for mounting the spiral-mandrel 32 a (or alternativeembodiments) thereon. Thus, in one embodiment of the method of thepresent invention, the wire 30 may be coiled around the mandrel 28forming a spiral-mandrel 32 (explained above). The mandrel 28 may or maynot be removed thereafter. If the mandrel 28 is not removed, the wire 30acts as a “spacer” to place a gap between the surface of the mandrel 28and the stent 10 for the purpose of polishing. Subsequently, the stent10 may be positioned onto the spiral-mandrel 32 forming a “stentspiral-mandrel assembly”. The stent spiral-mandrel assembly may then bemounted onto the device 38 for polishing. The stent 10 may thereafter besubjected to intense heat (indicated by arrows 42) via convection orradiation, or “heat flashing,” from a heat source 40 in order to roundout the sharp corners 22 of the stent struts 12 and the connectingelements 14 thereof. The heat source can be at a distance 0.25″ to 2.0″from the spiral-mandrel assembly, preferably 0.5″. The duration of theheat flashing can be between two and eight or ten seconds, preferablyapproximately five seconds. The duration depends on factors such as thematerial of the stent 10, the distance of the stent 10 to the heatsource 40 and the temperature used. The temperature of the heat can befrom about 40° C. to about 175° C., preferably about 55° C. to about 65°C.

In some embodiments, the stent 10 can be rotated (arrow 38 e) during theheating process so as to ensure even application of heat. For example,the stent can be rotated about 10 to about 3500 rpm, preferably about100 rpm to about 1000 rpm. In other embodiments, an area of the stent 10can be heated, following by termination of the heat, followed by adegree of rotation of the stent 10. Subsequently, the heat can beapplied again to a new segment of the stent and this process can berepeated. In other embodiments, the stent 10 can be moved longitudinally(arrow 38 f) while the heat is being applied. Yet, in other embodiments,the stent 10 can be heated, followed by termination of the heat,followed by moving the stent 10 longitudinally to expose a differentarea of the stent to the heat treatment. It should be understood thatany combination of the movements described above can be used for heatpolishing the stent 10 of the present invention.

The external heat source 40 may be from a heater coil, an Nd-YAG laser,a radio frequency (“RF”) heater or an apparatus for blowing hot air orgas (e.g., inert gas), for example. Moreover, the heat generated fromthe heat source 40 can be in a range between the glass transitiontemperature (“Tg”) and melting temperature (“Tm”) of a polymer. In someembodiments the heat generated can be equal to or greater than the Tg ofa polymer of the stent 10 and less than the Tm of a polymer of the stent10. In some embodiments, the temperature can be equal to or above Tm. Insome embodiments, the duration of exposure of such temperatures is ofsufficient time and under conditions so as to allow a temperature of thepolymer of the stent, mostly around the edges of the strut, to reach atemperature equal to or above Tg of the polymer. In some embodiments, itis preferable that the temperature of the polymer of the stent reach atemperature equal to or greater than the Tg of the polymer but notgreater than the Tm of the polymer. Should the stent be composed ofmultiple polymers, such temperature refers to the temperature of atleast one of the polymers that achieves the desired polishing of thestent. In this manner, the sharp corners 22 on both the abluminalsurface and the luminal surface of the stent 10 may be rounded out.

More particularly, the spiral-mandrel 32 a allows heat from the externalheat source 40 to reach the luminal surface of the stent 10 due to itshollow nature and the spacing between the coils (see FIG. 9A). That is,heat from the external heat source 40 will pass through the interstitialgaps 16 of the stent and through the spacing of the coils of thespiral-mandrel 32 a, ultimately reaching the lumen 44 (shown in FIG. 4C)of the spiral-mandrel 32 a. As such, the heat inside the lumen 44 willcirculate and contact the luminal surface of the stent 10, including atleast one sharp corner 22, resulting in the polishing thereof.

Alternatively, in the embodiment in which the spiral-mandrel 32 isformed from a heat conductive material, the heat transferred to thespiral-mandrel 32 from the heat source 40 may in turn be transferred tothe luminal surface of the stent 10, including at least one sharp corner22, resulting in the polishing thereof. In this manner, both the luminalsurface and the abluminal surface of the stent may be polishedsimultaneously.

In the alternative embodiment in which the mandrel 28 is not removed,the coils of the spiral-mandrel 32 a will act as a “spacer” between themandrel 28 and the stent 10, as illustrated in FIG. 9B. Thus, heat fromthe heat source 40 will pass through the interstitial gaps 16 of thestent and through the spacing of the coils of the spiral-mandrel 32 a,thereby accessing the luminal surface of the stent 10 resulting in thepolishing thereof.

FIG. 10A illustrates another embodiment of the method of the presentinvention, which method uses a conduit, such as a porous hypotube 46, topolish the stent 10. The porous hypotube 46 can have two open ends, asillustrated by FIG. 10A and a lumen 44 extending therethrough. In oneembodiment, the hypotube 46 can have one open end and one closed endwith the lumen 44 terminating at the closed end. Alternatively, thehypotube 46 can have both opposing ends closed, such that the lumen 44defines a hollow bore within the support structure. Such closed end(s)is mounted on a polishing system, such as the apparatus illustrated inFIG. 10B. The pores can be interconnected or discrete, and can extendthrough the body of the structure so as to allow for heat to exit outfrom the pores. The hypotube 46 may be heat conductive ornon-conductive, and can be stainless steel, aluminum, gold or anycombination thereof, for example. Moreover, the hypotube 46 may beformed from or coated with a substance, such as parylene or Teflon, toprevent the stent 10 from adhering to the hypotube 46 during thepolishing process. In this method, the heat source 40 may be internal tothe hypotube 46, such as, for example, a (very) small heater coil orcoils, or a heating pin capable of being inserted therein. The heat(shown by arrows 42) may therefore heat the stent 10 from within.Alternatively, the heat source 40 may be external to the hypotube 46,with the heat (shown by arrows 42) being transferred through a lumen 44and pores of the hypotube 46. In some embodiments, the heat source canbe generated from a heat source which heats a gas which is subsequentlyblown through the lumen 44 and out through the pores of the hypotube 46.The gas can be, for example, air or an inert gas. Once a stent 10 ismounted on the hypotube 46, the luminal surface of the stent will beexposed to heat from the heat source 40 either externally or internallyas described above. In this manner, the luminal surface of the stent 10is polished. It should be noted that for all embodiments describedherein, the heat source can be internal, i.e., in the lumen 44 of thespiral-mandrel 32 a, or any alternative embodiments 32 b, 32 c, 35, 35b, 46 or 48, or external. Certainly, in some embodiments, it can beboth.

A further alternative assembly is depicted in FIG. 10B generally at 47.In this assembly, the hypotube 46, which supports the stent, can bemounted on a spinning mechanism 47 a which spins the stent 10 relativeto a fixed heating source 40. The mandrel can be mounted in a chuck 47 bthat accommodates different diameters. The chuck 47 b in turn, can beconnected to a motorized mechanism wherein the rotational speed canthereby be controlled. One option is to couple it to a computer control,which allows for controlled axial movement 47 c into the heat source andcontrolled rotation thereof. In some embodiments, the stent 10 can berotated (arrow 47 d) during the heating process so as to ensure evenapplication of heat. For example, the stent can be rotated about 10 rpmto about 3500 rpm, preferably about 100 rpm to about 1000 rpm. In otherembodiments, an area of the stent 10 can be heated, following bytermination of the heat, followed by a degree of rotation of the stent10. Subsequently, the heat can be applied again to a new segment of thestent and this process can be repeated. In other embodiments, the stent10 can be moved axially (arrow 47 c) while the heat is being applied.Yet, in other embodiments, the stent 10 can be heated, followed bytermination of the heat, followed by moving the stent 10 axially toexpose a different area of the stent to the heat treatment. It should beunderstood that any combination of the movements described above can beused for heat polishing the stent 10 of the present invention.

FIG. 11 illustrates another alternative embodiment of the method of thepresent invention. In this figure, a “conveyor mechanism” 48 isillustrated with a plurality of stents 10 mounted thereon, in spacedrelation. In one embodiment, the conveyor mechanism 48 may be a form ofthe spiral-mandrel 32 a, though considerably longer, or a series ofmandrels connected in a spaced fashion relative to one another. Theconveyor mechanism 48, with a plurality of stents 10 mounted thereon,may be mechanically moved (depicted by arrow 50) towards a heat source40 for polishing of the stents. In an alternative embodiment, theconveyor mechanism 48 may be configured to suspend the stent 10 at bothends thereof in the air as the stents move toward (and away from) theheat source 40. It should be understood that the conveyor mechanism 48may be configured in a multitude of forms, with a principle goal thatthe conveyor mechanism 48 allows heat to pass through for the polishingof the luminal (and abluminal) surface(s) of the stent 10, in aconsistent and efficient manner. Further, the heat source 40 can definea heat polishing chamber through which the stent 10 passes by theconveyor mechanism 48. The stent may move at a continuous speed throughthe chamber, or at a slowed speed or even briefly stop for the heatpolishing step.

FIG. 12A shows generally at 49 an alternative system for heat polishinga stent 10 which can, for example, be mounted on a spiral-mandrel, asdiscussed above. The heat 42 from a heat source 40, such as a heatercoil, is applied to the stent radially via radiation or convection. Avariation of system 49 is shown by system 49 a in FIG. 12B. It showsthat the heat 42 from a heat source 40 can be forcibly applied throughtubes 49 b directed radially towards the stent 10. Tubes 49 b can bepositioned at equal distances around the stent 10 so that theapplication of heat 42 is evenly distributed. In some embodiments, theheat distribution is even across the length of the stent 10. An evendistribution of heat can be important for all embodiments for uniformityin polishing. Rotation and axial movement of the stent 10 during thepolishing process may certainly contribute to such uniform heatdistribution. In some embodiments, selective application of heat may berequired as some regions of the stent 10 may require more polishing thanothers. Accordingly, local and concentrated application of heat would bemore beneficial as opposed to heat treatment of the whole stent at once.

FIG. 13 illustrates yet another alternative embodiment of the method ofthe present invention. In this figure, a stent 10 is shown mounted on aheat conducting tube 52. In some embodiments, the heat conducting tube52 can be in intimate contact with the luminal surface of the stent 10.A heating element 54 may be located inside the lumen of the heatconducting tube 52. In some embodiments, the heating element 54 may be aheater rod which is, for example, electrically energized. In someembodiments, the heating element 54 can be in intimate contact with theheat conducting tube 52, as well. When heat is applied to the heatingelement 54, the heat is transferred to the heat conducting tube 52,which in turn is transferred to the luminal surface of the stent 10. Theluminal surface of the stent 10 is thereby polished, rounding out the“sharp corners” 22 of the stent 10 thereof. The construction andoperation of the heating element 54 and tube 52 can take many forms aswould be apparent to those skilled in the art.

An enlarged portion of a strut 12 of a stent 10 resulting from anembodiment of a method of the present invention is illustrated in FIG.14. After polishing, the strut 12 may still have a cross-section with a“square” shape with four surfaces, walls or sides 18 and four corners22; however, the corners 22 may be “rounded out”, i.e., changed from anangular to a non-angular configuration, due to heat treatment orflashing from the heat source 40 (see FIG. 15). In FIG. 15, across-section of strut 12 taken at line 15-15 of FIG. 14 illustratesthese features in greater detail. The polished strut 12 includes foursurfaces, walls or sides 18 and four rounded corners 22. Because thecorners 22 are rounded, the strut 12 is not as susceptible and may evenbe immune to cracks initiated by stress risers. Moreover, heat treatmentor flashing from the heat source 40 will only affect the surfacemorphometry of the stent 12, thus maintaining the integrity of the stentfor subsequent use.

As discussed before, crimping or expansion of the stent 10 subjects thestruts 12 and connecting elements 14 to stress, which may in turn causethe stent to crack. Together, FIGS. 16 and 17 represent an illustrativeexample of a crimping process as known in the prior art but used on astent polished according to the present invention. In FIG. 16, a stent10 is shown on a catheter 56 in an expanded state. By applying pressureto the outer diameter of the stent (shown by arrows 24), the stent 10 issecured to the catheter 56, or “crimped” thereon, and thereafter readyfor delivery into a bodily lumen. A stent is typically manufactured inan expanded state and may be crimped onto a catheter by a manufacturer,or, alternatively, may be left in an expanded state to be subsequentlycrimped onto a catheter by a user.

In FIG. 18, the stent 10 is shown in an expanded state during deliveryto a bodily lumen 58 using a balloon-expandable stent assembly. Itshould be understood that alternative stent assemblies, such as aself-expanding stent assembly, will subject the stent 10 to expansion asillustrated in this figure, within the bodily lumen. Thus, the presentinvention for polishing the entire surface of a stent, including theabluminal and luminal surfaces of the stent, substantially or completelyreduces or eliminates cracks caused by the crimping and expansionprocesses.

From the foregoing detailed description, it will be evident that thereare a number of changes, adaptations and modifications of the presentinvention which come within the province of those skilled in the art.The scope of the invention includes any combination of the elements fromthe different species or embodiments disclosed herein, as well assubassemblies, assemblies, and methods thereof. For example, instead ofa polymeric stent a non-polymeric stent or other type of device(including other types of implantable medical devices) can be used.Further, the stent or other device may be polished using solventsinstead of heat. The invention can further be used for application of anactive agent or drug. The active agent or drug can be embedded orcompounded in the body of the stent or disposed on the body as acoating. The coating can include a polymer carrier and preferably shouldbe deposited after the polishing process. It is intended that all suchvariations not departing from the spirit of the invention be consideredas within the scope thereof.

What is claimed is:
 1. A method of polishing a polymeric stent,comprising: mounting a stent made from a material including a polymeronto a structure having a series of gaps; and after the mounting,subjecting the stent to heat from a heat source so as to modify asurface morphometry of at least a section of the stent from an angularconfiguration to a non-angular configuration.